Ultra Lean-Electrolyte Li–S Batteries Realized by Highly Solvating Electrolyte Design

Lowering electrolyte usage is a key to attaining high energy density lithium–sulfur (Li–S) batteries. However, this remains a tremendous challenge in the conventional ether-based electrolytes with moderate polysulfide solubility. Highly solvating electrolytes, which can facilitate polysulfide dissolution, are considered a promising strategy to overcome this issue. They can also elevate sulfur utilization via altering reaction pathways and expediting redox kinetics. Nonetheless, mechanistic probing and kinetic evaluation on the complicated Li–S chemistry are still lacking. Herein, we design a highly solvating electrolyte via synchronous solvent and additive engineering. Spectroscopic investigations uncover that high-donor-number component can enable S₃^- radical-directed reaction path and three-dimensional Li₂S precipitation. Additionally, it has been revealed that ammonium ions promote the dissociation and dissolution of Li₂S by means of the H-S^2–bond. Benefiting from high polysulfide solubility and favored redox reaction, Li–S batteries with a low electrolyte and sulfur (E/S) ratio of 5 μL mg_s^–1 achieve a high capacity of 1092 mAh g^–1. Even at a harsh E/S ratio of 3 μL mg_s^–1, they still deliver an admirable capacity of 923 mAh g^–1and sustain a stable operation over 40 cycles. Our work elucidates the polysulfide speciation and reaction mechanism in highly solvating electrolytes, which opens a new avenue for achieving pragmatic lean-electrolyte Li–S batteries.